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Re: Question on "Seismic Zone Factor" (Z

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Regardless of the origin of the zone 2A classification, it's use in Hawaii
for the island of Oahu was based on analysis of the 10%/50year ground
acceleration value relative to the 0.15g criteria.  This has been
additionally verified during the National Seismic Hazard Mapping Project by
USGS which resulted in the NEHRP mappings used for new(2%/50) and
existing(10%/50) structural design spectral accelerations.

Gary Chock
Hawaii State Earthquake Advisory Board

At 05:02 PM 5/25/00 -0700, you wrote:
>        A federally-funded 1978- vintage NEHRP precursor, ATC 3-06,
>"suggested" this way, and the 1982-88 SEAOC Seismology Committee followed
>suit, for the  1988 UBC seismic sections. Reportedly there was code
>adoption-endangering "political" resistance in Zone 2 territory in the US
>Midwest to the O.2 factor, and as a sop to them, a member of Seismology
>Committee in the fall of 1986 offhandedly suggested dividing Zone 2 into A
>and B portions, with the reduced value in the eastern portion (2A) that you
>have noted. This gambit was embraced eagerly, and it worked. 
>There was no known technical research whatsoever as backing for the Zone 2
>split or the .15 factor. This I know, because I was the one who suggested
>the idea in committee.
>It's hard to tell what in seismic code isn't fictitious or hastily
>concocted, and then sold as solid, accurate science and time-proven wisdom
>to eager believers. 
>At least this Zone 2A stunt didn't add needless workload to code users, or
>add interpretation quandaries. To my amusement, Zone 2A has sprouted up in
>Arizona and Hawaii since originally appearing east of the Rockies. 
>Charles O. Greenlaw SE  Sacramento CA

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